Add sorting functionality to workspace GraphQL queries with a new WorkspacesOrderBy enum
MR: Pending
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## Description
As part of our [new designs for Workspaces](https://gitlab.com/groups/gitlab-org/-/epics/18674), we need to add comprehensive sorting functionality to workspace GraphQL queries so that users can sort workspaces by various criteria. This implementation will also provide a foundation for future admin interface improvements and enable enterprise admins to leverage this API for reporting and automation tools.
## Acceptance criteria
- [ ] Create new `WorkspacesOrderBy` enum with following sorting options:
- [ ] `CREATED_AT` - sort by workspace creation time
- [ ] `UPDATED_AT` - sort by last workspace update (backing field for "Recent Activity")
- [ ] `NAME` - sort by workspace name alphabetically
- [ ] `ACTUAL_STATE_UPDATED_AT` - sort by when workspace state last changed
- [ ] `PROJECT_ID` - sort by project ID (GraphQL API only, not exposed in UI)
- [ ] `PROJECT_NAME` - sort by project name
- [ ] `USER_ID` - sort by user ID (GraphQL API only, not exposed in UI)
- [ ] `USER_NAME` - sort by user name
- [ ] Implement sorting logic in workspace Finder class
- [ ] Add `orderBy` field to all existing workspace GraphQL queries
- [ ] Update GraphQL schema documentation for all enum values
## TODO: Implementation plan
## Technical Notes
**Implementation Reference:** [Refer this comment from @cwoolley-gitlab](https://gitlab.com/gitlab-org/gitlab/-/issues/562370/designs/sortdropdown.png#note_2702232410)
Sorting with project name & user name would require conditional join with the respective table in the ActiveRecord query.
**Future Benefits:** This GraphQL sorting capability will support:
- Current workspace list UI improvements
- Future admin interfaces for workspace reporting
- Enterprise admin custom reporting and automation tools
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